World War One was the commencement major conflict that saw the utilization of airplanes. During the early on years of the fighting , aircraft were by too large used for surveillance too observation , only every bit the state of war progressed , airplanes took on an offensive role. By the terminate of the state of war , airplanes had larn too thus deadly that it became necessary for the Allies to develop novel tactics for air defence forcefulness , if the side past times side state of war was to live won.
The most of import part of an effective air defence forcefulness organization is an early on alert organization that could uncovering too rail enemy aircraft earlier they arrive. But inward the days earlier radar , the alone means to uncovering enemy aircraft was to nous to the audio of approaching airplanes.
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The Royal Air Force established a serial of listening posts closed to the coasts of Great Britain. They consisted of huge spherical , concrete reflectors called “sound mirrors” that were able to amplify the dissonance of storey engines every bit they approached over the English linguistic communication Channel , past times reflecting audio waves off their curved surfaces too concentrating them to a focal betoken , similar rays of lite reflecting off a curved mirror. Devices similar this are frequently found inward scientific discipline museums today every bit “whispering galleries”.
Several microphones were placed inward front end of the reflector too depending on which microphone received the strongest signal , the direction of approach of the storey could live determined.
By the terminate of the 1920s , the commencement audio mirror went upward at Hythe , inward Kent , on the S coast of England. The location was chosen because it savage nether the flying path of commercial aircraft heading towards French Republic , thereby providing sufficient exam subjects. At commencement , at that spot were 5 concave mirrors made of steel too concrete , each half dozen to nine meters high. These mirrors could efficiently amplify audio waves having wavelength upward to iii feet. But the audio waves the armed forces was interested inward had wavelengths of xv to eighteen feet.
In 1930 , the 6th too terminal mirror was erected. It was a huge curved wall , sixty meters long too 8 meters high. With a listening make of nigh xx miles , it was this mega-mirror that lastly delivered the required results.
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At 1 time construction of audio mirrors started along the coast from Norfolk downwards to Dorset , to brand it impossible for enemy planes to approach the Britain from the English linguistic communication Channel undetected. In add-on to the mirrors , a huge squad of to a greater extent than than 500 people were trained for rapid too accurate communications required betwixt the listening postal service , telephone operators too officers inward the command room too at headquarters.
But airplanes were becoming faster , which meant that past times the fourth dimension they were detected they would already live likewise closed to bargain with. Soon doubts nigh the audio mirror projection began to arise. Then inward 1935 , the projection came to an acute end. The option to the audio mirrors — Radio Detection too Ranging , or radar for short— had been perfected.
The concave audio mirrors , that never saw activeness , nonetheless stands closed to the English linguistic communication coast. The most famous of these mirrors are at Denge , nigh Dungeness , inward Kent , England. The site has iii mirrors —a 60-meter-long curved wall , a 9-meter circular dish too a 6-meter dish.
Sound mirrors stand upward inward at to the lowest degree xix unlike places , including Republic of Malta which is the alone house exterior Britain to bring these structures.
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Photo credit: Greg/Flickr
Photo credit: Paul/Flickr
Photo credit: Paul/Flickr
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Sources: Wikipedia / www.andrewgrantham.co.uk / www.spiegel.de